OF ANATOMY AND PHYSIOLOGY

in their structure, except that the amount of connective tissue was excessive compared to that noted in other animals. Large, coarse trabecule ran through the gland, and, dividing into finer processes, made compartments enclosing groups of parathyroid cells. These latter,. which were of the usual polygonal type, showed no special tendency to stain deeply with eosin.

of work has been done on the comparative anatomy of the parathyroids, most investigations have, not unnaturally, been restricted to the more easily obtained bodies of domestic animals. Sandstr6m (16), the first to describe the parathyroids, dissected the dog, cat, rabbit, horse and ox, and in each concluded that there was one parathyroid to each thyroid lobe. Baber (1) examined many thyroids and described in those of the dog, cat, and pigeon "undeveloped areas" of VOL. XLII. (FOURTH SER. VOL. I.)- JAN. 1908. thyroid tissue, and his account of these appears to tally with that of Sandstrtm's parathyroids, with this distinction, that whereas the latter described the parathyroids as isolated by connective tissue from the thyroid beneath, Baber states that his areas might be not distinctly separated from the rest of the gland. Horsley (9) and Rogowitsch (15) confirmed the occurrence of embryonic tissue in association with the thyroid. Kohn's (11) research is of special value in that it led to the conclusion that there were normally two parathyroids on each side in the dog, cat, rabbit and guinea-pig, one on the lateral and one on the tracheal surface of each thyroid lobe. This discovery derived its importance from the fact that hitherto operators had not taken into consideration the possible existence of more than one gland on each side.
During the past ten years the subject has been taken up by Gley (7), Nicolas (13), Cristiani (3), Vassale and Generali (19), Moussu (12), Verdun (20), Simon (18),Groschuff (8), Ver Eecke (21), Easterbrook (4), Prenant (14), Capobianco and Mazziotti (2), Torretta (18a), Alquier (la), Berkeley (2a), Rogers and Ferguson (14a), Jeandelize (10) and others, who, in addition to the animals already mentioned, examined the monkey, fox, goat, pig, horse, seal, bat, rat, mouse, and some birds. They agree that the parathyroids number four, except in some species where only two are present. So constant are these numbers stated to be that Groschuff goes so far as to suggest a classification of mammals into two divisions according to whether the parathyroids are two or four. Recently Vincent and Jolly (22) examined the glands in certain animals in the course of experiments on the effects of parathyroidectomy. In dogs, cats, monkeys, rabbits, prairie-wolves and badgers they recognize two parathyroids on each side and in the rat only one. To a study of the glands in the guinea-pig they devoted considerable time, with the result that they found the number and position of the parathyroids to be extremely variable, as many as six occurring in one animal.
As regards the position of the parathyroids they have generally been described as lying, the external on the lateral surface of the thyroid, the internal on the tracheal surface, often depressed in the main gland but always separated from it by connective tissue. They vary in position between limits. In animals with only two parathyroids it is the internal one that is stated to be absent, while the external parathyroid in the rabbit was found by Gley (7) to be commonly 5 mm. posterior to the thyroid applied against the carotid artery; but he mentions that in this animal parathyroids may be wholly absent on one side of the neck. In the goat the external parathyroid is stated to lie in contact with the deep surface of the submaxillary gland (12). Moussu (12) has noted the occurrence of supplementary parathyroid glands in the dog, though Jeandelize (10) doubts their existence. Shaper (17) states that in the sheep he has very frequently found nodules with a parathyroid structure near the bifurcation of the common carotid, and others, two, three or more, along the course of the carotid. Jeandelize (10) has confirmed this statement.
A study of the literature on the subject forces one to the conclusion that few if any of the authorities quoted have protected themselves from the criticism that they allowed their unaided eye to attempt what only the microscope could effect. It is admitted that the parathyroids are exceedingly difficult to find, that it is possible to mistake them for lymphatic or accessory thyroid glands, and that they may be buried deeply in the thyroid lobes. Yet sufficient attention has not been paid to these facts. If parathyroids often possess no naked-eye characteristic whereby they can be identified, no attempt to enumerate them will be successful unless every glandular body found within wide limits of the thyroid is subjected to microscopic examination. Except, perhaps, for Vincent and Jolly's work (22) on the parathyroids of the guinea-pig, there has been, as far as I can find, no such detailed quest undertaken. Occasionally, though rarely, accessory parathyroids have been described, but since Kohn's work in 1895 four parathyroids have been looked on as the greatest number present.
In the present research 77 animals, comprising 42 mammals and 35 birds, have been examined. The procedure adopted was as follows:-The neck of each animal was carefully dissected and every glandular body, no matter how small, and including all on the surface of the thyroid, was subjected to microscopical examination. The thyroid itself, if small, was examined by serial sections, but if large was cut into thin slices, the surfaces of each of which were scrutinised with a lens and all suspiciouslooking pieces retained for microscopical examination. In brief, the guiding principle followed was to regard every gland as a possible parathyroid, and none has been identified except by its microscopical features.
This detailed search has led to conclusions at variance with those already quoted, and from the following pages it will be found that the parathyroids vary widely in number in different species and even in different members of the same species. An instance of this is afforded by three specimens of the Green Monkey (C. callitrichuts) in whom the parathyroids numbered 1, 1 and 8 respectively. Further, the existence of parathyroid tissue in the thyroid, not isolated by connective tissue, has been found to be of much commoner occurrence than was anticipated.
It is not proposed in this paper to do more than record the details relating to each animal or bird examined. The explanation of the facts and the conclusions to be drawn from them will be reserved for consideration in a subsequent paper (6), when they can be taken in conjunction with facts already established concerning the human parathyroid glands (5). For the present it will be sufficient to draw attention to the broad conclusion that even in the same species the parathyroids are subject to variations in number and in position, and it is probable that in no mammal at any rate is the number of parathyroids constant. Further, parathyroid tissue is commonly present in the thyroid, and intermediate types are readily found both in the thyroid and in accessory glands, with the result that the identity of some bodies has often presented difficulty. Under these circumstances it might have appeared undesirable to retain the two expressions thyroid and parathyroid; but since the histological distinction between the two is widely recognised and is a convenient one, it was found advantageous to employ both in the following descriptions. This usage is not to be taken as an assent to the proposition that there is a functional difference between the thyroid and the so-called parathyroid glands. In the following pages a gland which presented the gross anatomical features of a thyroid will be spoken of as a thyroid even though its structure is wholly or in part parathyroidal, while those smaller accessory glands which were partly vesicular and partly non-vesicular will be regarded as thyroidal or parathyroidal according to which type of structure preponderated.
Appended is a classified list of the mammals and birds that have been examined, and of whose thyroids and parathyroids a description is given. Before passing to the special accounts of the glands in the various animals some general remarks on the thyroid and parathyroids in mammals will be prefixed. A similar introduction concerning birds will be reserved until that group is under consideration.
1. Position, etc., of the Thyroid in Mammals.-The thyroid gland, which is invariably present, lies on either side of the anterior 1 part of the trachea, I The terms " superior," " inferior,"' " anterior," "posterior," which have been used in the paper on the Human Parathyroids (5) in conformity with the custom of human anatomists, are here replaced by "anterior," "posterior," "ventral," "dorsal," respectively, following the practice of comparative anatomists. and as a rule overlaps the posterior end of the larynx. The lobes vary considerably in shape, but usually present a convex external or lateral surface and a concave internal or tracheal surface. They are pale or dark brown in colour, and much more regular in outline than in man. They may or may not be connected by an isthmus, but this process is variable even in the same species. The lobes are usually of equal size, but one or other may be the larger. Not uncommonly they are prolonged posteriorly as a tail-like process running in the interval between the trachea and esophagus. Accessory thyroids are found in many animals. Occasionally colloid cysts are met with.
2. Number, Position, etc., of Parathyroids.-Isolated glands possessing a parathyroid structure were found in most but not in all the members of the series. When present their total number was two, three, or four; but these numbers were exceeded in certain specimens. A two-spotted paradoxure (Nandinia binotata) and a fossa (Cfryptoprocta ferox) each had six; a Green Monkey (Cercopithecus callitrichus) eight, and a collared Fruit Bat (Cynonycteris collars) ten. As will be explained immediately, there was often great difficulty in deciding whether a particular gland was to be called accessory thyroid or parathyroid.
The parathyroids can scarcely be said to possess any definite anatomical relations, so widely do their positions vary. The commonest site of occurrence was on the convex lateral surface of the thyroid; but they were also found on the tracheal surface, or sunk in the thyroid either deeply or just beneath the capsule or in the immediate neighbourhood of the thyroid, either dorsal, anterior, posterior or external to it, or some distance remote, either isolated or in association with accessory thyroids or lymphatic glands.
They present no naked-eye feature by which their identity can be established; and over and over again in this series they have been found unexpectedly on microscopical section. Those examples which have been attached to lymphatic glands or accessory thyroids have often been quite minute, and frequently glands too small for macroscopic identification have been found attached to the capsule of the thyroid on serial section being made of the whole.
The total volume of parathyroid tissue bears no constant relation to the total volume of thyroid tissue.
3. Structure of the Thyroid.-The structure of the thyroid is sufficiently well known to require no detailed attention here. From the enveloping connective-tissue capsule trabeculao pas; through the gland, dividing it into a series of polygonal compartments, each of which encloses a vesicle consisting of a single layer of regular cubical epithelial cells arranged round a central cavity containing colloid. Bloodvessels and lymphatics run in the trabeculse.
So far as the connective-tissue framework and the vessels are concerned, this description holds good for all the animals in this series. It is in the contents of the compartments that differences appear. In most mammals these contents conform to the account already given, but frequently the chambers are found to be occupied by solid masses of polygonal cells whose protoplasm may be clear, not staining with acid dyes, or may be full of oxyphile granules. Types intermediate between these extremes are readily found.
A chamber thus filled may be found standing alone amid an uninterrupted expanse of vesicles, or may form one of a small collection, as in a specimen of the Spotted Ichneumon (Herpestes aurcpunctatus).
Sometimes an appreciable proportion of a section is occupied by these polyhedral cells, as in the Sumatran Civet (Viverra tangalunga), while occasionally glands were found in which these masses considerably exceeded in total area the thyroid vesicles: such was the case with the Arabian Gazelle (Gazetla arabica) and the European Beaver (Castorfiber). In the Fat-tailed Desert Mouse (Pachyutromis duprasi) the whole thyroid was made up of those unarranged cells.
Not infrequently there could be noticed among the cells of a compartment a distinct attempt to become grouped round a central lumen; and according to the extent of the transformation, so the cells were found to lose their polyhedral shape and approximate to the regular cubical type. As will be shown immediately, these masses of polyhedral cells are similar in structure to those composing the parathyroids; and since accessory thyroids may show the same variations of structure as the parent gland, the difficulty already referred to of selecting the correct term, "thyroid" or " parathyroid," to apply to these bodies is obvious. As a matter of practice the tissue, thyroid or parathyroid, which predominated decided the question, but an organ which was anatomically the thyroid was always regarded as thyroid even though its structure was that of a parathyroid.
Cells, similar to the polyhedral cells just described and presenting the same variations in appearance, were frequently found lying between the vesicles. They occurred either singly or in small clusters, and will be referred to as interstitial or parathyroid cells. They possess the same characters as the cells of a parathyroid as regards shape, nucleus, protoplasm and oxyphile granules.
4. Structure of the Parathyroids.-The connective-tissue elements of the parathyroid are planned on the same lines as those of the thyroid but on a more delicate scale. A thin capsule gives off fine trabeculae which divide the whole gland into polyhedral compartments. The bloodvessels and lymphatics run in this framework.
The compartments are all, or nearly all, filled with solid masses of polygonal cells whose protoplasm may be pale and clear or filled with oxyphile granules, or intermediate between these extremes. Often the cells may be seen to have begun to arrange themselves around a lumen filled with a drop of colloid, and thus a primitive vesicle is formed. Occasionally a perfectly formed vesicle, lined by a single layer of regular cubical epithelium and containing colloid, is met with. Colloid also occurs among the polyhedral cells even when no attempt at orderly arrangement is evinced, and in some specimens this secretion may be seen in large masses distending lymphatic vessels.
Finally, a few small isolated glands from the neighbourhood of the thyroid were found to be vesicular on the surface but parathyroidal beneath. Such have been reckoned, not as accessory thyroids, but as parathyroids.

PRIMATES.
Eight specimens of this order, representing five species, were examined. In the Black Ape there was on each side one parathyroid and one accessory thyroid, the latter corresponding to each other in position. The tissue of the left parathyroid was in places directly continuous with that of the thyroid. The White-collared Mangabey showed two parathyroids and Campbell's Monkey one on each side. The Pig-tailed Monkey possessed on the right two parathyroids, one at the posterior pole of the thyroid and one at the centre of the lateral surface; and on the left two, one at the middle of the lateral surface, the other posterior to the thyroid. Behind the right lobe an accessory thyroid lay between the trachea and the esophagus.
Three specimens of the Green Monkey differed notably from each other. In the first the only parathyroid found was buried in one thyroid lobe; in the second, one accessory thyroid and eight parathyroids were found, two on the right lobe, three on the left, and three in the neighbouring connective tissue; the third specimen had one accessory thyroid on the right and two on the left, one of the latter being associated with a parathyroid. BLACK APE (Cynopithecus niger). The thyroid lay oil either side of the anterior part of the trachea, the lobes being connected across the 5th and 6th rings by a thin, transparent isthmus 2 mm. broad. The right lobe, which tapered somewhat anteriorly, disclosed a large cyst occupying its posterior quarter. Three smaller cysts were seen on the tracheal surface. A pale-coloured parathyroid lay on its lateral surface near the anterior pole, while half-way along the ventral border was an accessory thyroid. An artery ran to the posterior pole and a second entered on the dorsal part of the tracheal surface, one-third down the lobe.
The left lobe was shorter and thicker than the right, and contained no cysts. There was an accessory thyroid in a position corresponding to that on the right and a parathyroid on the posterior part of the tracheal surface.
Microscopical Appearances.-Thyroid and accessory thyroid: Arrangement of connective tissue normal. The structure was vesicular throughout, but many of the follicles were irregular in outline (compressed, triangular, tri-radiate, or stellate), and all were lined with tall columnar epithelium. The colloid was scanty and granular, and many vesicles contained nucleated cells. A few interstitial cells lay between the vesicles.
The parathyroids consisted of irregularly arranged columns and clumps of cells. There were no vesicles and no colloid. The left parathyroid was imperfectly cut off from the subjacent thyroid tissue, with which it was in places directly continuous.
GREEN MONKEY (Cercopithecus callitrichus). Specimen No. 1.-The thyroid gland was made up of two elongated ovoid bodies lying in the usual position. No isthmus connected the lobes. A parathyroid was found in the centre of one lobe, but none appeared on the surface.
Microscopical Appearances.-The thyroid was divided in the usual way by connective tissue septa. It was vesicular throughout, the vesicles being lined by regular cubical epithelium and containing colloid. There were very few interstitial cells between the vesicles. At the posterior pole of one lobe, beneath its capsule, was found a clump of lymphoid tissue.
The parathyroid consisted of a mass of polygonal cells with a supporting connective tissue framework in which many bloodvessels ramified. There was no attempt at vesication. For the greater part of its circumference it was isolated from the circumjacent thyroid tissue, but at one part this barrier was absent and the two tissues were directly continuous.
Specimen No. 2.-The thyroid was of peculiar shape. Each lobe lay at the side of the trachea covering the posterior third of the thyroid cartilage, the cricoid cartilage, and the first six tracheal rings. A narrow isthmus connecting the lobes spanned the trachea at its third ring. The posterior extremity of each lobe was prolonged into a tail of greater length than the lobe itself, reaching as low as the 16th ring, and being thinner and more diffuse than the thyroid proper. These tails were united about the 12th ring by a second isthmus (P1. 1. fig. viii.).
An accessory thyroid gland was found in the immediate neighbourhood of the thyroid gland.
Parathyroids. -Altogether eight parathyroids were discovered-two on the right thyroid, three on the left, and three in the connective tissue between the thyroid lobes and the carotid vessels. Of those on the right, the larger was situated at the anterior pole of the thyroid, the smaller half-way along its tracheal surface. The three on the left lay one at each pole, and the other at the middle of the dorsal border.
Microscopical Appearances.-Thyroid: The greater part of the section showed normal thyroid structure-vesicles lined by cubical epithelial cells and filled with colloid-but there was much interstitial or parathyroid tissue. This latter occurred either as a small collection of a few cells between vesicles, or as larger masses of cells, or as extensive areas free of vesicles, but in each case directly continuous with the thyroid tissue (i.e. not encapsuled by connective tissue). In a few examples the parathyroid cells showed some slight attempt at vesicle-formation.
The colloid itself, for the most part homogeneous, was here and there granular.
The accessory thyroid showed similar characters to the parent gland.
In all eight parathyroids the cells were massed irregularly without any definite formation, but they showed varying degrees of activity. Five of them were in full activity, the cells being large, with granular protoplasm which was strongly eosinophile. Two were resting, their cells being smaller, staining only feebly and with no granularity. In one the majority of the cells were resting, but a few active areas occurred.
One of the active glands was attached to a lymphatic gland, and showed a large mass of colloid in one of its lymphatics, while another parathyroid had attached to it a small nodule of lymphoid tissue.
Specimen No. 3.-The thyroid was in its usual position, and each lobe, which was small in comparison with the size of the animal, tapered slightly towards its posterior pole. The two lobes were united across the trachea by a broad thin isthmus, and the left was prolonged posteriorly into a short tail of connective tissue terminating in a pale gland (? parathyroid, but specimen lost).
When the thyroids were removed there appeared on the right side one, and on the left two accessory thyroids lying on the carotid vessels, and one of the latter had a small parathyroid on its surface.
Microscopical Appearances.-The thyroid showed the usual structure, with a fair number of interstitial cells, and the accessory thyroids differed ill no way histologically from the main gland.
The parathyroid consisted of a mass of polyhedral cells.
WHITE-COLLARED MANGABEY (Cercocebus collarss. The thyroid lay in the normal situation, broadening out posteriorly. On the lateral surface of one lobe close to the anterior pole a parathyroid was found. A second was placed close to the posterior pole.
Microscopical Appearances.-Thyroid: Usual connective-tissue compartments. The whole organ was vesicular, the follicles lined by regular cubical epithelium, and containing colloid, often granular. Very few interstitial cells lay between the vesicles except where the latter were very small, but even here they were limited in number.
The parathyroid cells were arranged without order for the most part, but here and there showed a distinct approach to vesicular grouping. No colloid was found CAMPBELL'S MONKEY (Cercopithecus Campbelli). The thyroids occupied a somewhat unusual position. The lobes broadened anteriorly and ran much farther forward than is customary, extending up on each side of the larynx so that their upper ends lay under shelter of the lower jaw. There was no isthmus, but each lobe was continued backwards for about 1-5 cm., the prolongation showing alternating light and dark bands corresponding to the rings of the trachea, and produced by pressure of the latter on the former.
The right lobe showed a parathyroid on its lateral surface as a pale circular area flush with the thyroid. The left lobe showed no corresponding gland, but just anterior to the junction of the thyroid with its prolongation on its ventral border appeared a parathyroid (P1. I. fig. x.) Microscopical Appearances. -The thyroid presented the usual structure, with a varying number of interstitial cells; in some places they were absent, in others they were present in clumps.
The parathyroids showed the usual structure, the protoplasm of the cells being faintly granular.

PIG-TAILED MONKEY (Macacus nemestinus). (Age at least 16 months.')
The thyroid gland occupied the usual position, and there was no isthmus. The right lobe was somewhat peculiar in shape, tapering anteriorly to a blunt extremity, but widening behind to give a triangular outline. The left lobe was quadrilateral in shape.
A small accessory thyroid, dark in colour, came into view when the right lobe was removed, lying in the interval between the trachea and esophagus.
Half-way along the lateral surface of the right lobe, deeply sunk in it but easily dissected off, lay a parathyroid pale in tint. At the posterior extremity of the dorsal margin a second parathyroid, bilobed, lay embedded in fat. About the centre of the lateral surface of the left lobe was a parathyroid similar to the one on the right, while a second parathyroid appeared in the connective tissue a short distance behind the posterior pole.
Microscopical Appearances.-The thyroid was vesicular in structure. At the surface of the gland the vesicles were all large, lined with cubical epithelium, and filled with homogeneous colloid, and no interstitial cells were present. Deeper, however, the vesicles, though of similar structure, were small, and were separated from each other by a considerable number of interstitial cells. In many instances the connective-tissue compartments were filled with solid masses of these cells, there being no central cavity and no colloid.
The accessory thyroid resembled the main gland in structure. The parathyroids presented the customary features.

CHIROPTERA.
Only one example of this order was examined-a Collared Fruit Bat. In this animal certain parts of the thyroid gland had definite parathyroid structure. The left lobe showed one large and three small parathyroids superficial to its capsule, and in the centre of the right lobe was a mass with exclusively parathyroid characters isolated by connective tissue, and another on the capsule. Four lymphatic glands lying in close proximity to the thyroid lobes all showed parathyroid tissue attached to their surfaces. COLLARED FRUIT BAT (Cynonycteris collaris). (Age 7 years and 3 months.) An elongated oval, each lobe of the thyroid lay against the anterior part of the trachea with no connectant isthmus. On the right side, lateral to the thyroid, lay two lymphatic glands side by side, the posterior pole of the internal one being pale and white. On the left side were two similar lymphatic glands, the median one being in contact with the thyroid.
Microscopical Appearances.-The thyroid, divided by connective tissue in the usual manner, was composed of small vesicles of uniform size, which were lined by regular cubical epithelium and filled with colloid. In some compartments there was no central cavity, the cells being aggregated into solid clusters as in a parathyroid. In certain parts the whole appearance was that of a parathyroid gland, vesicles being completely absent. Embedded in the centre of the gland and isolated by connective tissue was a mass of cells which were indistinguishable from a parathyroid. Another small parathyroid lay on the surface of the gland. Each of the lymphatic glands showed on section small clumps of parathyroid tissue attached to the surface of the capsule.
The left lobe of the thyroid showed the same peculiarities of structure as the right. Depressed on its surface and enveloped in the same capsule was a fair-sized parathyroid, while three minute clusters of paratlhyroid tissue were found superficial to the capsule. Each lymphatic gland showed parathyroid tissue on its surface.

CARNIVORA.
Eighteen examples of carnivorous animals, representing fifteen species, were examined.
Of the Felidae, the Serval showed one parathyroid on each side, not corresponding to each other in position, and the Fossa (P1. I. fig. iv.) five parathyroids and an accessory thyroid on the left, and one parathyroid attached to an accessory thyroid on the right. Five out of the six parathyroids contained colloid.
The family of Viverridoe (small cats) afforded seven representatives. The African Civet Cat had one parathyroid on each side, and the cells of one of them showed a distinct tendency to form vesicles. The Sumatran Civet was without any parathyroid proper, but the structure of the thyroid was as much parathyroid as thyroid. The Feline Gennett presented no parathyroid on the surface of the thyroid, but deep in the centre of one lobe was an isolated parathyroid, which contained one or two vesicles containing colloid. Three specimens of the Two-spotted Paradoxure differed strikingly from each other. The first showed three parathyroids on the right and one on the left, while both lobes of the thyroid itself had the histological features of a parathyroid except under the capsule, where ordinary thyroid vesicles abounded, and also in the centre of the right gland, where a mass of typical thyroid tissue occurred. The second specimen had no parathyroids, and the thyroid showed the usual follicular structure, with clusters of interstitial or parathyroid cells in those situations where the vesicles were smallest. In the third specimen six parathyroids were found-three on a side-and the thyroid had much the same structure as the last specimen. The Malayan Paradoxure had no parathyroid on either side, but the majority of the compartments of the thyroid were filled with inasses of parathyroid cells, especially near the posterior pole of the right, where vesicles were entirely absent. Slight attempts at the formation of follicles were not rare. Of a couple of Spotted Ichneuinons the first had no parathyroid, the second three (two on one side). The former had a normal thyroid with a few clusters of parathyroid cells, but the second presented extensive areas with parathyroid features, though many fields were made up of ordinary thyroid follicles. The Suricate, with one parathyroid on each side, had a thyroid almost wholly parathyroid in structure, but at rare intervals, least infrequent at the surface, occurred small vesicles. Colloid filled these, and also lay in drops among the parathyroid cells.
The Spotted Hyvena (P1. I. fig. vii.) possessed a thyroid with very unequal lobes each with cysts, and only the left had a parathyroid. The Sidestriped Jackal had a single mass of parathyroid tissue embedded in each thyroid lobe directly continuous with the surrounding thyroid tissue; in addition a parathyroid lay on the surface of the left lobe. In the Weasel no parathyroid was discovered, and the thyroid, though chiefly vesicular, had some compartments with parathyroid attributes, and others intermediate in type between thyroid and parathyroid. The family of ProcyonidteT were represented by the Kinkuajou and the Cunning Bassaris (Raccoon). In the former the thyroid was deeply placed against the esophagus dorsal to the trachea, and each lobe was accompanied by a parathyroid, one of the latter containing colloid in lynmphatic spaces. The Raccoon with no parathyroid on the left, though possibly some on the right videe linfra), showed a peculiar thyroid whose vesicles had convoluted walls and were filled with much colloid, which was also found occupying lymph channels.
Cystic swellings were the most noticeable naked-eye feature of the thyroid of the Malayan Bear, and they occurred freely throughout both lobes (PI. I. fig. ix.). Parathyroids, bright yellow in colour, were found to the number of three on the left and one on the right. In addition, a fourth glandular body, paler than the thyroid, less yellow than the parathyroids, was found in connection with the left lobe, and its sections proved to be as, much thyroid as pairathyroid. The microscopical appearances of the thyroid were remarkable, partly for the duplication of the secreting membranes of the vesicles, partly for the alternation of areas of large vesicles with a fair number of interstitial cells with areas of minute vesicles with qualmtities of these cells, SERVAL (Felis serval). The thyroid lobes lay in the usual position, and were not united by any isthmus. The right lobe was pear-shaped, tapering posteriorly, while the left was more slender and slightly larger.
One parathyroid was found in contact with each lobe-on the right at the junction of the middle and lower thirds of the dorsal border, on the left near the anterior pole one quarter along the dorsal border.
Microscopical Appearances.-The thyroid was made up of a mass of small, evenlysized vesicles lined by regular cubical epithelium, and only a few had any colloid content. Between the vesicles were a few interstitial cells.
The parathyroids were normal.

FOSSA (Cryptoproctaferox). (Age at least 14 years.)
The thyroid stretched from the posterior limit of the larynx back for 16-18 rings. There was no isthmus, and each lobe was brown, diffuse, and very soft in texture. Both lobes tapered considerably towards their posterior ends, and the left was prolonged as a diffuse tail of connective tissue, containing four small collections of parathyroid tissue (P1. I. fig. iv.).
No parathyroid was seen on the surface of the lobes. On the right carotid artery at the level of the middle of the thyroid gland appeared a pale, elongated, accessory thyroid divided by two shallow constrictions and having perched on its anterior pole a small parathyroid. On the left side, in a corresponding position, was a smaller accessory thyroid almost wholly occupied by a cyst, and just anterior to it a small parathyroid.
Microscopical Appearances.-The thyroid was made up of vesicles lined generally by cubical cells, but often by flattened cells, and containing much colloid. Colloid was also found in irregular spaces between the vesicles. In those areas where the vesicles were lined by flattened cells interstitial cells were entirely absent, but in other parts they occurred in small amount. The sections were those of a gland in active secretion. In one or two places the appearance to be noted below as regards the thyroid of the Malayan Bear was observed, namely, small vesicles lying immersed in the colloid of a large vesicle.
Both the accessory thyroids contained large cystic collections of colloid. The structure of the parathyroids presented nothing peculiar. The cells were large, and stained well with eosin. The four parathyroids in the tail of the left lobe were all active. Three of them contained a considerable amount of colloid, and one consisted of a large mass of colloid with comparatively little parathyroid tissue around. The parathyroid attached to the right accessory thyroid showed a large collection of colloid.

AFRICAN CIVET CAT (Viverra civetta). (Age at least 71 years.)
The thyroid lobes were connected across the 3rd and 4th tracheal rings by a very narrow isthmus arising from the extreme posterior pole of the left lobe, but somewhat more anteriorly from the right. The left lobe showed a depression in the posterior third of its lateral surface, in which lay a white coloured parathyroid gland bound down by connective tissue. The right lobe showed no body in the corresponding position, but in the connective tissue 2-3 mm. anterior to the oral pole of the thyroid was a white-coloured parathyroid (PI. I. fig. v.).
Microscopical Appearances.-The vesicles of the thyroid varied much in size, were lined by regular cubical epithelium, and contained colloid. There were many clusters, large and small, of interstitial cells.
The parathyroid on the left showed the usual structure, but in that of the right there was a distinct tendency for the cells to be arranged in concentric manner (not, however, enclosing colloid), their shape being more or less cubical.

SUMATRAN CIVET (Viverra tangalunga). (Age at least 31 years.)
Each thyroid lobe lay in the usual site, and was elongated and irregular in shape, tapering towards its posterior pole. A narrow isthmus joined the extreme posterior poles (PI. I. fig. vi.).
No parathyroid or accessory thyroid was found. Microscopical Appearances.-The thyroid consisted of as much parathyroid tissue as thyroid tissue. There was a number of vesicles of varying size, filled some with homogeneous, some with granular colloid, and all lined with perfectly regular epithelium. Between the vesicles was a considerable amount of parathyroid tissue, the cells arranged for the most part without order, but often showing an attempt at concentric formation. Here and there between the parathyroid cells were droplets of colloid.

FELINE GENNETT (Genettafelina). (Age at least 18 months.)
The thyroid occupied the usual position and no parathyroid was found, except one in the centre of one of the thyroid lobes.
Microscopical Appearances.-Only one thyroid lobe was examined. On section it was seen to be made up of vesicles lined by regular cubical epithelial cells and containing colloid. In places the vesicles were very small, but at the surface they were for the most part large. A few interstitial cells were scattered through the sections, and were most numerous between the smallest vesicles.
Sections passing through the centre of the gland disclosed a parathyroid deeply embedded. It presented the usual histological features -a connective tissue compartition supporting clumps of polyhedral cells staining brightly with eosin, but was of interest because of the presence of one or two vesicles containing colloid.
TWO-SPOTTED PARADOXURE (Nandinia binotata). ,Specimen No. 1 (age at least 18 months).-The thyroid occupied the usual position. Its lobes were connected across the trachea by a narrow isthmus, and each was prolonged posteriorly into a fine tail of diffuse texture, that on the left terminating in a small lymphatic gland.
On the lateral surface of the right lobe one-third the way along the dorsal border lay a small parathyroid. A second parathyroid projected from the same border near the posterior pole, while the tail was made up of parathyroid tissue. The left lobe showed one-third along the dorsal border a parathyroid, pale in colour like the others.
Microscopical Appearances.-The thyroid was made up of absolutely typical parathyroid structure, the cells being massed together with no attempt at order. On the surface of the gland, however, there was definite conversion into vesicular thyroid tissue, the follicles being lined with regular cubical epithelium and filled with homogeneous colloid. Over the greater extent of the surface these vesicles were only one layer deep, but in places they penetrated farther into the gland. In the centre of the right gland, wholly buried, was a mass of typical thyroid tissue with, however, many interstitial cells between the vesicles. 'This clump, which was distinguishable even to the naked eye, was directly continuous with the parathyroid tissue around, no connective tissue being interposed.
The parathyroid bodies were similar in appearance, being composed of masses of polyhedral cells with much granular protoplasm staining well with eosin.
Both thyroid lobes showed the same features, but there was no central clump of thyroid tissue in the left.
Specimen No. 2.-The thyroid filled the usual position. No parathyroid gland was found.
Microscopical Appearances.-The thyroid consisted of vesicles lined by regular cubical epithelium and containing colloid. In a few vesicles the epithelium was more nearly flattened. Certain areas showed the epithelium of adjacent vesicles separated only by the finest layer of connective tissue, but the majority of the fields revealed a varying number of interstitial cells. These clusters varied in size, being largest and most frequent where the vesicles were smallest. At the surface of the gland, where the vesicles were big, the clusters were rarest, and in many places completely absent, The lining cells, in the largest follicles especially, tended to a flattened type. Near the centre of the gland was a large mass of colloid in a cavity lined by definitely flattened epithelium (i.e. a lymphatic vessel). Specimen No. 3 (age at least 18 months).-The thyroid lobes were situated as in the previous specimens and were connected by an isthmus. The right showed a whitish parathyroid attached loosely to its lateral border about one-third from the anterior end. From its posterior pole grew an elongated tail of connective tissue which contained near its end another whitish parathyroid. Close to the posterior pole and ventral to the carotid artery lay a third parathyroid, differing from the others, however, by its yellow hue.
The left lobe presented a parathyroid near the anterior extremity of the lateral border. A connective-tissue tail similar to the one on the right terminated in a second parathyroid, while a third was found near the posterior pole.
Mlicroscopical Appearances.-The thyroid showed the usual vesicular structure, with a fair number of interstitial cells. The larger collections of colloid near the surface were contained in spaces lined by distinct flattened endothelium (i.e. lymphatic vessels.) The parathyroids presented the customary features.
MALAYAN PARADOXURE (Paradoxus hermaphrodites). The thyroid lobes occupying the usual position were not united by an isthmus. No parathyroid could be found.
Microscopical Appearances.-The thyroid was divided into compartments by connective tissue, but a somewhat curious appearance was given to the sections in places, owing to the isolation of areas by thick trabeculhe, whereby a lobular structure was conferred on the gland. Many of the compartments were lined by regular cubical epithelium enclosing colloid, but the greater number showed an irregular massing of cells as in a parathyroid. Near the posterior pole of the right thyroid the vesicles were completely absent, and the structure was typical of a parathyroid without colloid. This area was directly continuous with the thyroid proper. A VOL. XLII. (FOURTH SER. VOL. I.)-JAN. 1908. 12 second similar area was seen on section of the left thyroid at the surface of the gland.
In certain of the compartments where, as already mentioned, the cells were irregularly massed an attempt at the formation of a definite lining epithelium could be traced.
SPOTTED ICHNEUINMON (Herpestes auropunctatus). Specimen No. 1.-Tbe thyroid lobes call for no comment beyond the fact that they were not united by an isthmus. No parathyroid was found.
Microscopical Appearances.-The thyroid showed the usual vesicular structure, with a few clusters of interstitial cells here and there. Microscopical Appearances.-The thyroid showed a structure more nearly parathyroid than thyroid in nature. The majority of the compartments were filled by polygonal parathyroid cells with no attempt at regular arrangement or the formation of central cavities. Other compartments, constituting a fair proportion of the whole, possessed a definite lining of cubical cells and a central lumen containing colloid either granular or homogeneous, but extensive areas were readily found in which there was no suspicion of thyroid structure, the whole field being typically parathyroid.
The parathyroids themselves were wholly embryonic and yet differed from the main gland in certain respects. Their general appearance was paler, owing to the cells being less crowded. The protoplasm of each was considerable, quite pale in tint and slightly granular in texture. The nuclei, oval in shape, were longer and paler than most of those in the thyroid l)roper, and were made lip of a more open chromatin network. These differences between thyroid and parathyroid probably represented different stages in functional development.
Buried in the centre of one lobe was a small cluster of these larger cells, -encapsuled from the thyroid around. It appeared in only a few serial sections, as it was made up of not more than a couple of hundred cells. SURICATE (Suricata tetradactyla). (Age at least 9 months.) The thyroid lobes, oval in shape, were joined by an isthmus. At the anterior extremity of each on the dorsal border was a small parathyroid. Lateral to each thyroid lobe was a bright orange-coloured gland which proved to be lymphatic in nature.
Microscopical Appearances.-Sections of the thyroid revealed fine trabeculae of connective tissue forming compartments, each filled with a mass of polyhedral parathyroid cells. Rarely, but with greater frequency near the surface, were small areas throughout which the cells had grouped themselves around colloid-containing cavities, and had acquired a cubical shape by mutual pressure. None of these vesicles attained large size. Intermediate types where drops of colloid lay among the irregularly arranged cells were also noted. Further, a few large masses of colloid were found enclosed by a more or less regular layer of cubical cells.
The parathyroids were very similar to the thyroid, but the protoplasm of the cells was paler, and no colloid could be found. SPOTTED HYENA (Hycena crocuta). (Age at least 10 years.) The thyroid lobes, which were joined by an isthmus across the 4th, 5th, and 6th rings of the trachea, were markedly different in configuration. The right, which was four or five times the volume of the left, was iiotched at its anterior end, where it received an artery, and its outline somewhat resembled that of a large bean. The isthmus arose by a broad root from the whole of the lower half of its ventral border. The lateral surface of the lobe showed an elevation due to a cyst, and on its tracheal surface were three indistinctly outlined nodules of thyroid tissue. No parathyroid was found (P1. I. fig. vii.).
The left lobe was long and thin, and the isthmus arose from the posterior extremity, so that the whole presented the appearance of an " L." Two cysts projected from the lateral surface near the posterior pole, and a third was seen on the tracheal aspect. About the middle of this latter surface was a parathyroid distinctly white in colour and separated from the thyroid beneath by connective tissue.
Microscopical Appearances.-Post-mortem changes were marked. The thyroid showed the usual structure, but most of its vesicles were empty. Here and there were large vesicles containing colloid, and not infrequently cysts similarly occupied. Interstitial cells were scattered irregularly throughout the organ.
The parathyroid presented the normal features. The connective tissue, which was fairly abundant, formed coarse trabeculve dividing the gland into lobule-like portions.

SIDE-STRIPED JACKAL (Canis lateralis). (Age at least 3 years.)
The thyroid occupied the usual position. The right lobe was the longer of the two, being prolonged posteriorly into a tapering process. There was no isthmus.
The left lobe showed depressed on its lateral surface a pale parathyroid. In a corresponding position on the right was a curious finger-like process of thyroid tissue. On section a mass of parathyroid tissue was found embedded in each gland, directly continuous, however, with the surrounding thyroid tissue.
Microscopical Appearances.-The lining cells of the thyroid vesicles were cubical and the colloid homogeneous. The walls of the vesicles showed a marked tendency to become convoluted and to project into their lumina.
The parathyroid presented no unusual feature.

WEASEL (M1ustela vulgaris).
The thyroid was somewhat pear-shaped, the tapering end being posterior. There was no isthmus.
No parathyroid was found. Microscopical Appearances.-The thyroid was permeated by the usual connectivetissue trabecule. Many compartments thus formed contained vesicles lined by regular cubical epithelium, and containing homogeneous colloid. In others the cells lay in disorder, while in others again they showed only a tendency to group themselves around a central lumen.
KINKAJOU (Cercoleptes caudivolvulus). (Age at least 31 years.) The thyroid lobes were reached only on deeper dissection than customary, as they lay dorsal to the trachea and in lateral contact with the esophagus. There was no isthmus. Each lobe tapered posteriorly and revealed deep to its posterior end a parathyroid yellow in colour.
Microscopical Appearances.-The thyroid was of usual structure, and its vesicles of uniform size and lined with cubical epithelium. The colloid contents were much vacuolated, but this appearance was probably artificial. The parathyroids possessed the usual structure, and one showed two masses of colloid contained in lymphatics on the surface of the gland.
CUNNING BASSARIS (RACCOON) (Bassariscus astuta). (Age at least 5 years.) The position of the thyroid gland calls for no comment. Its lobes were united about their middles by a thin, delicate isthmus.
No parathyroid was found on the left side. On the right a pale gland was attached to the surface of the thyroid near its anterior pole, and was perhaps a parathyroid, but unfortunately the specimen was lost before being sectioned.
Microscopical Appearances.-Sections of the thyroid presented a striking appearance, owing to the vesicles being either very large or very small, and the former being notably irregular in outline. All the follicles were lined by cubical epithelium, and the gland was in a state of active secretion, as shown by the large amount of colloid present. The large vesicles, instead of being regular in shape, possessed walls which bulged and receded ini most irregular fashion, while in many of them the secreting surface was amplified by the projection into the lumen of long and delicate folds of connective tissue bearing on both surfaces cubical secreting cells. This arrangement gave many of the vesicles a lobulated aspect, while in others the appearance was as if there was continuity of colloid between two adjacent vesicles. The small vesicles were all regular in outline (circular or oval), and presented no foldings of their walls. Here and there were lymphatic channels lined by flattened epithelium and containing colloid, one in particular being found split longitudinally for some considerable distance. Interstitial cells were fairly numerous between the small vesicles, but were rare elsewhere.
MALAYAN BEAR (Ursus malayanus). (Age at least 18 months.) The thyroid gland was large in comparison to the size of the animal, and its lobes lay on either side of the lower part of the larynx and the upper six or eight rings of the trachea. They were joined at their posterior ends by an isthmus formed of a broad, flat sheet of thyroid tissue. Their colour, was dark brown (P1. 1. fig. ix.).
The left lobe was the longer and larger of the two. Its oral pole was notched and its outline was regular, except for a few local prominences. The two largest of these projected from the dorsal margin, and others appeared on the tracheal surface, on the lateral surface, and on the isthmus. In each case the swelling was found to be caused by cystic formations. On the lateral surface of the lobe lay a parathyroid -a pale, bright-yellow, oval body about 1 cm. in length-and farther back was a second smaller parathyroid, also bright-yellow but bilobed. On the same surface near the anterior pole a minute body was found, yellowish in hue but less so than the parathyroids, though paler than the thyroid tissue proper. This proved to be in structure intermediate between thyroid and parathyroid. A third gland somewhat similar in appearance found in the connective tissue posterior to the lobe proved to be a lymphatic gland.
A considerable part of the anterior pole of the right lobe was -occupied by a large dark-coloured cyst. About the middle of the lateral surface was a bright yellow parathyroid. There were two irregular prominences of thyroid tissue projecting from the dorsal border of the gland. Microscopical Appearances.-The gland was fixed entire for twenty-four hours and then cut into thin slices, the surfaces of each being carefully examined. No additional parathyroid was found, but the whole gland was seen to contain a large number of colloid cysts of divers sizes.
The microscopical appearances of the thyroid varied considerably in different sections. For the most part it was that of a thyroid composed of large polygonal vesicles lined by regular cubical cells and filled with homogeneous colloid, while in between the vesicles was a fairly large number of interstitial cells. In places occurred clumps of minute vesicles with a considerable amount of interstitial cells admixed, and here the features were as much those of a parathyroid as of a thyroid. Such clumps showed in marked contrast to the more open aspect of the remainder of the sections, and were in some, but not in all cases, isolated by connective tissue.
In many places large irregular masses of colloid occurred between the vesicles, especially where the latter were minute, and these collections of secretion were not contained in any definite follicle, but occupied intercellular spaces. In other places the epithelial walls of the vesicles were markedly convoluted, the folds projecting into the lumen within. Where this condition was marked there was produced the appearance sometimes noted in Graves's disease, where a cluster of colloid-containing vesicles will be found lying in the midst of the colloid content of a large vesicle. In a few instances the colloid, instead of being homogeneous and dark-staining with eosin, was granular and pale.
The whole appearance of the thyroid was that of a gland in very active secretion. The minute body found on the lateral surface of the left lobe was more parathyroid than thyroid in structure, one end consisting of small, regularly-formed vesicles, the other of parathyroid tissue with a few very minute vesicles.
The parathyroids presented no unusual feature in their structure, except that the amount of connective tissue was excessive compared to that noted in other animals. Large, coarse trabecule ran through the gland, and, dividing into finer processes, made compartments enclosing groups of parathyroid cells. These latter,. which were of the usual polygonal type, showed no special tendency to stain deeply with eosin.
UNGULATA. Examination was made of six different species of Ungulata. The Collared Peccary, representing the family of Suidrn or Pigs, was found to possess no parathyroids.
The three examples of the Bovidrn were specially interesting. The Beatrix Antelope, with no isolated parathyroid, showed a thyroid which was entirely embryonic in structure-there was no attempt at vesicle formation and no secretion of colloid. The Arabian Gazelle also, with no isolated parathyroid, showed a curiously-shaped thyroid which possessed a parathyroid structure although a considerable number of vesicles were present. In a Four-horned Antelope the thyroid was remarkably small and its compartments were filled with polyhedral, embryonic-looking cells, but at a few sites there was a commencing transformation into thyroid follicles. A gland resembling the thyroid and found near the left lobe was composed of similar cells except at the surface, where there was a cortical layer of small thyroidal vesicles.
The Cape Hyrax was found to possess one parathyroid on each side, and its thyroid was unique in that it sent a process between the esophagus and trachea. In the Barbary Wild Sheep the thyroid was supplemented by two accessory thyroids attached to the thymus at the root of the neck, one of them being of greater volume than both the thyroid lobes together. The structure of all these was for the most vesicular (some follicles had tall columnar cells), but there was much parathyroid tissue. No parathyroid was found.
The thyroid was found lying at the side of the trachea covering the first few rings and extending forward to spread over the hind border of the cricoid cartilage. The lobes expanded posteriorly, where they united across the trachea by a narrow isthmus.
Fourteen glands from the neighbourhood were found and examined, but no parathyroid or accessory thyroid was discovered.
Microscopical Appearances.-There was much post-mortem change. The thyroid was vesicular throughout, its follicles being lined with regular cubical epithelium, and containing colloid.
BEATRIX ANTELOPE (Oryx Beatrix). On removing the sterno-hyoid and sterno-thyroid muscles the thyroid was seen as a small gland lying at the side of the 2nd, 3rd, and 4th tracheal rings. Each lobe was regularly pear-shaped, the larger end being anterior, and was attached by connective tissue to the side of the trachea. No trace of any isthmus was made out, nor did a minute dissection reveal any glandular body on or near the thyroid gland.
Microscopical Appearances.-Longitudinal sections of both lobes of the thyroid showed a uniform appearance. TIhe whole section was divided by connective tissue into compartments, each of which was occupied by a mass of cells irregularly arranged. Nowhere was there any trace of vesicle formation, and there was no colloid. The sections were indistinguishable from parathyroid tissue.
ARABIAN GAZELLE (Gazella arabica). Each lobe, the site of which conformed to normal, consisted of a head about 2-5 cm. long, passing at the posterior pole into a long tail 4 cm. long on the right and 6 cm. long on the left. The shape of the whole lobe suggested that of a spermatozoon.
No parathyroids were found. Microscopical Appearances.-Sections through each lobe showed the structure to be for the most part non-vesicular. The gland was divided by thin connective-tissue strands into compartments, by far the largest number of which were occupied by masses of polyhedral cells. Scattered irregularly, but not very infrequently, were compartments lined by regular cubical epithelium set around colloid. Such vesicles varied in size, but none was of notable diameter. The whole organ was peculiarly vascular: in many places there were areas consisting solely of spaces filled with red corpuscles.' It is not possible to say whether the sections are those of a thyroid with parathyroid characteristics or of a parathyroid with thyroid features.

FOUR-HORNED ANTELOPE (Tetraceros quadricornis). (Age I month.)
The thyroid lobes were small and lay on either side of the trachea, their posterior ends being united by an isthmus. At the posterior pole of the left lobe were two translucent bodies not found on the right side videe inJfra).
The gland was of a very pale brown, almost white, colour, and its lobes showed no irregularity (If outline. The tracheal surface was concave to fit against the windpipe, and the lateral surface convex, with no prominences or fissures. The most noteworthy point in its naked-eye appearance was its remarkably small size compared to that of the whole animal.
Microscopical Appearances.-Sections through the whole length of each gland revealed the following characteristics: The gland was enveloped in a connective-tissue capsule, and its substance was divided into compartments by a delicate meshwork of trabeculue, in which were the smaller bloodvessels and capillaries. Each compartment was filled with embryoniclooking cells, polyhedral in shape, with a considerable amount of faintly granular protoplasm staining readily with eosin, and with nuclei circular or oval.
In addition to this uniform structure there was to be seen in a few places the commencing change of this embryonic tissue into mature thyroid tissue. This transformation was seen to begin as an increase of the eosinophile affinity of the cells occupying a compartment. A small space filled with a coarsely granular, pale-staining secretion then appeared in their midst, and around it the cells. still polygonal in shape, became grouped in layers two or three deep. Later, this space gradually enlarged and the cells became more regularly arranged, until finally they formed a single layer next the connective tissue wall and enclosed a circular or oval central cavity. By mutual pressure these cells lost their polyhedral outline and became regularly cubical. The central cavity was finally occupied by a drop of homogeneous colloid.
In the young antelope examined, only a very small part of the total gland had lost its embryonic character, but the change had gone far enough to allow all the above changes to be followed.
Of the two translucent bodies mentioned above, one was mislaid, but the other showed a structure exactly comparable to that of the thyroid. It consisted of similar compartments filled with polyhedral cells, but the conversion to thyroid structure was more advanced, though it was limited to the cortical regions of the gland. Almost the entire circumference showed a cortex of thyroid vesicles, in some places as many as six or eight deep, and the transformation was apparently 1 Three adjacent glands, presumably heemo-lymphatic, taken from near the bifurcation of the internal jugular vein, and black and spherical when fresh, presented this marked vascular character. spreading more deeply into the gland. They were all small, some incompletely formed, and still lined by more than one layer of cells, and with a few exceptions, where the content was homogeneous colloid, contained granular secretion.
CAPE HYRAX (Hyrax capenris). (Age at least 2 years.) The thyroid lobes lay at the side of the posterior part of the larynx and first few tracheal rings, and were united near their anterior ends by a narrow isthmus. Each was prolonged in an exceptional manner as a process passing in between the trachea and Esophagus, being firmly attached to the dorsal surface of the former. This arrangement made the removal of the glands particularly difficult. The two processes were united across the middle line by a transversely running vein (P1. I. fig. i.).
On each side a pale-coloured parathyroid was found lying on the lateral surface, that on the left being at the point of entry of an anterior thyroidal artery, on the right just posterior to this.
Microscopical Appearances.-There was the usual arrangement of connective tissue in the thyroid. Its vesicles, which varied greatly in size, were lined by regularly arranged cells varying in shape from a squat cubicle to a fairly tall columnar. The extreme types were as a rule single cells flanked by the more customary cubical cells. The vesicle contents were either homogeneous or granular colloid, but in many follicles the central part of the secretion was homogeneous, the periphery granular. There was a great number of interstitial cells which were large and polygonal, with much protoplasm, generally granular: they occurred for the most part in large clusters.
The parathyroids were made up of a mass of cells similar to those found in the thyroid clusters. They nowhere presented any definite arrangement, but many capillaries appeared among them. The whole appearance was similar to that of the human parathyroid in an active state.
BARBARY WILD SHEEP (Ovis tragelaphus). (New-born.) The thyroid lobes, which were small, lay on either side of the trachea and were not united by any isthmic tissue. At the root of the neck was a large thymus gland the anterior end of which was prolonged into two hornlike processes running up the neck ventral to and on either side of the trachea. Sunk in the substance of the median aspect of the left horn was a pale brown accessory thyroid gland measuring 1 cm. by *5 cm., while deep in order of dissection (i.e. dorsal) to the main mass but peeping from beneath it was a second accessory thyroid gland of greater volume than both the thyroid lobes put together (P1. I. fig. ii.).
No parathyroid was found. Microscopical Appearances.-The lobes showed for the most part thyroid structure, but there was much parathyroid tissue throughout. Many vesicles, probably the majority, were lined by cubical epithelium, but a large number, especially of the larger ones, showed regular, tall columnal cells. The colloid was more often pale and granular than homogeneous, the latter occurring most frequently in the smaller follicles.
Both the accessory thyroids agreed structurally with the thyroid proper.

RODENTIA.
This order is represented by ten specimens comprising seven species. In the Fat-tailed Desert Mouse the whole thyroid was parathyroid in structure, no vesicles having formed. On the surface of one lobe was an isolated mass of similar structure. The thyroid of a Dormouse, though showing the usual vesicles, had many clusters of interstitial cells. The European Beaver, with an unusually-shaped thyroid, had no isolated parathyroid, and though the main gland was to a certain extent vesicular, this arrangement was exceeded in amount by parathyroid tissue, amid the cells of which colloid frequently occurred. Both the Prairie Marmot and the Chinchilla had thyroids of normal structure, and the latter possessed a parathyroid attached to one lobe. The Golden Agouti with two parathyroids, one on each side, showed on the left an accessory thyroid which, though chiefly thyroidal in nature, was made up at one end of parathyroid tissue.
Microscopical Appearanres.-Each thyroid consisted throughout of parathyroid structure. [he cells, large, polygonal, with granular protoplasm, were arranged in irregular clumps and made no attempt to form vesicles. At intervals a drop of colloid was seen, but never with any definite arrangement of cells around.
On the surface of one thyroid, isolated by connective tissue, was a mass of cells having the appearance of a parathyroid. These cells were somewhat darker than those of the thyroid beneath, but this was due to the comparatively small amount of protoplasm, which resulted in the deep-stained nuclei being more closely apposed. DORMOUSE (Myoxus avellanarius). The thyroid was closely attached to the trachea. It was ill-defined in outline, and being of a remarkably soft consistency it is possible some fragment may have been left behind. In any case no parathyroid was found.
Microscopical Appearances.-The thyroid showed the usual follicular structure, but there were many clusters of interstitial cells. At one place there was a clump of large interstitial cells with granular protoplasm staining well with eosin.
EUROPEAN BEAVER (Castorfiber). (Age at least 2 years.) The position of the thyroid was normal. Its lobes were roughly globular in shape and less flattened than in most animals. They showed facets on their surfaces where the organ had been impressed by adjacent structures, and were united by a specially long and ribbon-like isthmus slightly indented at its middle (P1. I. fig. iii.). A large number of glands of varying shape and size were found in the neck, but they all proved to be lymphatic.
Microscopical Appearances.-Sections through the whole lobe showed that though the structure was that of a thyroid, there was an amount of parathyroid tissue greatly in excess of the thyroid proper. The vesicles, which varied greatly in size, were lined by a beautifully regular cubical epithelium, and contained colloid, either homogeneous or granular, and many gradations between the two were to be found. The parathyroid cells were of the usual type, and in places showed attempted arrangements into vesicles. Drops of colloid occurred frequently between these parathyroid cells. RED-BELLIED SQUIRREL (Sciurus variegatus). (The animal had been dead for some days before being examined, and postmortem changes were so marked as to render microscopical examination futile.) The thyroid was bright pink in colour, and lay on either side of the trachea and thyroid cartilage. A delicate isthmus united the lobes, but the gland was too soft and friable for further examination.

PRAIRIE MARMOT (Cynomis ludovicianus).
The thyroid lay at the side of the trachea, scarcely overlapping it at all. There was no isthmus. The anterior poles of the lobes were thin, tapering, and gelatinous.
About a quarter along the lateral margin of the right lobe a pale area was seen. It was minute in size, and was possibly a parathyroid, but was lost in preparation.
Microscopical Appearances.--The connective-tissue trabecule of the thyroid were somewhat thick, and in places the gland was infiltrated with fat. (The rodent had died at the end of the autumn, when about to hibernate, and the body showed everywhere a copious deposit of fat.) The general structure was vesicular, with regular cubical epithelium and much colloid. The follicles varied in size, some being small enough to be enclosed by less than a dozen cells; others were large. The anterior pole of one lobe showed only a collection of very large vesicles, the epithelium being either flattened or stunted cubicle. Interstitial cells were few, except where the vesicles were minute.
CHINCHILLA (Chinchilla lanigera). The thyroid extended from the posterior border df the thyroid cartilage to the 7th tracheal ring, and tapered slightly towards the posterior poles. There was no isthmus.
At the junction of the anterior and middle thirds of the internal margin of the left lobe there was a prominence made by a parathyroid gland.
Microscopical Appearances.-The structure of the thyroid was normal. The vesicles were all filled with homogeneous secretion, and much colloid was seen in the lymphatics running in the trabeculke. Clusters of interstitial cells, large and small, were seen scattered through the gland.
The parathyroid consisted of an irregular massing of cells with a slight suggestion of vesicle formation.
GOLDEN AGOUTI (Dasyprocta aguti). (Age at least 5 years.) The thyroid presented no feature of note. On the surface of one lobe was a parathyroid, and another was found in the centre of the other lobe.
Just below and ventral to the thyroid lobe was a small cyst containing drops of colloid. Ventral to the middle of the left lobe was an accessory thyroid.
Mlicroscopical Appearances.-The thyroid vesicles were lined by the ordinary cubical epithelium, and contained colloid. A fair number of interstitial cells lay between the follicles. The accessory thyroid showed chiefly thyroid structure, but at one end there were no vesicles, and the cells were arranged as in a parathyroid.
The parathyroid, which was isolated from the thyroid, consisted of solid masses of cells with no vesicles. A second parathyroid was found in the centre of one lobe, where it was isolated by connective tissue and associated with a buried mass of lymphatic tissue.

MARSUPIALIA.
Although three marsupials were dissected, in one the examination was not completed microscopically.
In the Vulpine Phalanger three accessory thyroids were found, one of which was associated with a mass of parathyroid tissue. The Short-headed Phalanger was without either accessory thyroids or parathyroids. VULPINE PHALANGER (Trichosurus vulpecula). The thyroid calls for no comment. Two millimetres behind its posterior pole lay a small accessory thyroid, disc-shaped, while another similar body lay on the 1st tracheal rilm, at the side of the trachea. In the connective tissue near the right lobe of the thyroid a third accessory thyroid was found.
M11icroscopical Appearances. -The thyroid possessed the usual capsule with trabeculae dividing the whole organ into compartments, most of which contained cubical epithelium grouped around a central cavity; a few, however, showed an irregular arrangement of cells. There was very little colloid.
One of the accessory thyroids presented at one extremity a mass of parathyroid tissue isolated from the rest of the gland by connective tissue.
SHORT-HEADED PHALANGER (Petaurus breviceps). (Age at least 3 years.) The thyroid lobes, which were not united by any isthmus, lay on either side of the anterior part of the trachea, ventral to the carotid vessels but wholly internal to them. To naked-eye examination they were plainly vesicular.
No parathyroid gland was found. Microscopiral Appearances.-Sections of the thyroid showed the usual appearance, most of the follicles being of large size and lined by short cubical (in many cases almost flattened) epithelium, and filled with much colloid. In a few places were groups of very small vesicles. Two or three clusters of parathyroid or interstitial cells were found, but no isolated parathyroid. DORMOUSE PHALANGER (Dromicia nana). (Age at least 41 years.) The thyroid was in the usual position and had no isthmus. There was a number of minute glands adjoining the thyroid lobes, but all the specimens were unfortunately lost.
[The table of references will be given at the end of Part II.] esophagus.